Imaging vibrationally mediated photodissociation dynamics of MgCl

Abstract

Magnesium monochloride (MgCl), a reactive intermediate in high-temperature combustion and plasma chemistry, has been theoretically recognized as a promising candidate for laser cooling. However, its key molecular parameters—such as bond dissociation energy, vibrational frequency, and excited-state topography—remain unclear due to inconsistencies between experimental and theoretical results. Here, we directly observe the photodissociation of MgCl molecules in the coupled electronically excited 42Σ+ and 52Σ+ states via developing laser-ablation molecular beam and time sliced ion velocity imaging techniques. By analyzing the vibrationally state-resolved velocity of recoiling magnesium atoms from the photolysis of MgCl at 193 nm, we determined a bond dissociation energy of 29 464(110) cm−1 and a vibrational frequency of 435(61) cm−1 for MgCl(X2Σ+). The measured dissociation energy serves as a lower bound for D0 and is notably higher than prior reported data, indicating that vibrational excitation effectively reduces the energy required for bond dissociation—a plausible reason for the underestimations observed in earlier measurements. Insights into the dissociation energy and dissociation dynamics of MgCl provide a key experimental basis for advancing theoretical models of reactive intermediates and prospective applications in laser cooling.